noun
hard-to-please person; grouch; complainer
Describes someone who is habitually difficult to satisfy, often complaining or finding fault. Similar to 気難し屋.
See also: 気難し屋
うちの上司はむずかし屋で、何をしても文句を言う。
Our boss is a hard-to-please person; he complains no matter what you do.
彼女はむずかし屋だから、プレゼントを選ぶの
She's such a grouch that choosing a present for her is tough.
Very similar in meaning; 気難し屋 emphasizes a moody or temperamental nature, while むずかし屋 focuses more on being hard to please.
Compound of むずかし (difficult, hard to please) and 屋 (person with a certain trait). The exact derivation of むずかし is uncertain, but it is related to 難しい (むずかしい).